Production web processes are used to fabricate a number of film and sheet products such as personal hygienic articles, disposable bags, napkins, packaging films and other articles. The films used in these processes have various purposes, but producers often perceive an opportunity to decorate the products or otherwise mark them by printing directly onto these plastic surfaces. These plastics are often very tough to print on and often require off-line printing with special auxiliary processes that provide durable printed images. These articles are also often produced on complex continuous production web processes that are designed for maximum production efficiency. Article producers generally prefer to integrate as many portions of the article assembly processes within these production web processes including article printing, but in-line printing methods are difficult to provide due to the problems with attaining good adhesion on these substrates as well as the integration costs associated with modifying existing production lines and the production efficiency losses that would ensue using current printing methods. Hence there is a need for in-line printing methods that can provide printed images on films with easy integration into existing processes and without reduction in production efficiency.
One of the most effective ways to provide in-line printing is via digital ink jet printing. In ink jet printing, printing is accomplished without contact between the printing device and the substrate on which the printed characters are deposited. Briefly described, ink jet printing involves projecting a stream of ink droplets to a surface and controlling the direction of the stream, e.g., electronically, so that the droplets are caused to form the desired printed image on that surface. This technique of noncontact printing is well suited for application of digital content such as variable decorative marks onto a variety of surfaces including porous and non-porous surfaces.
One of the most common forms of ink jet for marking products in production is CIJ (continuous ink jet) that includes both single and array-nozzle printers. CIJ printers can deliver a wide range of ink jet ink formulations that serve various industrial applications. However, current CIJ inks do not have sufficient adhesion to flexible films nor can they pass some of the basic durability requirements for the film industry.